Not sure why they went with a sci-fi version of all the origins and villain plans. Why wasn't he magician or rather illusionist and some other motive like trying to fund family member's surgery or something. Mysterio could've had redemption story at the end.

Because they had to reveal Peter's identity - they could've made it so Mysterio had a partner in crime who was actually evil and be mad that Mysterio turned good, then in rage reveal both Mysterio's and Peter's identity. I have no idea why MCU stories have gotten out of hand with less relatable and grounded. Spider-Man's supposed to be the very grounded and relatable but not in the MCU it seems.